1. Field of the Invention
This invention relates to a method for altering the surface catalytic activity of a porous crystalline zeolite (e.g. of the ZSM-5 type) in the cationic, e.g. hydrogen, form which involves the sequential steps of loading said zeolite with molten paraffinic wax sufficient to block all channels thereof, contacting the wax-loaded zeolite with hydrogen fluoride solution, and then calcining the hydrogen fluoride solution contacted zeolite.
2. Description of Prior Art
The use of zeolites as catalyst components is well known. Nevertheless, zeolites have been the subject of extensive investigations to improve their catalytic properties. Zeolites ZSM-5 and ZSM-11, for example, are fully described in U.S. Pat. Nos. 3,702,886 and 3,709,979, respectively, wherein it is disclosed that because of their ordered, porous structure, creating small interconnected cavities, they are selective toward certain molecules and provide catalytic capabilities for various chemical conversion reactions. U.S. Pat. Nos. 4,088,605 and 4,148,713 disclose a process combination wherein zeolites of the ZSM-5 type have their outer shells altered so as to be essentially aluminum-free, leading to a more selective catalyst. However, no known art discloses or suggests modifying the surface of porous zeolites such as those of ZSM-5 type by altering their surfaces and the alpha activity of the surfaces and thereby altering their catalytic properties by the present method.
It is noted that U.S. Pat. Nos. 3,354,078 and 3,644,220 relate to treating crystalline aluminosilicates with volatile metal halides. Neither of these latter patents, however, is concerned with altering surface activity of porous zeolites such as ZSM-5 type in the cationic form as in the present method. In fact, the use of hydrogen fluoride with aluminosilicates has been avoided because of resulting lattice damage. Hydrogen fluoride in high concentrations, e.g., 5 N or greater, readily attacks both silica and alumina. Lower concentrations may also damage lattice structures if contact is maintained for too long a time. With some zeolitic materials, hydrogen fluoride treatment under controlled conditions has been used to alter pore size. U.S. Pat. Nos. 3,997,474 and 4,054,511 relate to altering effective pore size of natural ferrierite ore with very dilute hydrogen fluoride treatment. When the same treatment of erionite was conducted, a large loss in activity and crystallinity resulted.